Hostname: page-component-6bb9c88b65-x9fsb Total loading time: 0 Render date: 2025-07-27T01:44:44.989Z Has data issue: false hasContentIssue false
  • English
  • Français

Petrogenesis of Ordovician igneous rocks in the southern part of the Welsh Basin

Published online by Cambridge University Press:  01 May 2009

R. E. Bevins ,
G. J. Lees  and
R. A. Roacht
R. E. Bevins
Affiliation:
Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF1 3NP, U.K.
G. J. Lees
Affiliation:
Department of Geology, University of Keele, Keele, taffs ST5 5BG, U.K.
R. A. Roacht
Affiliation:
Department of Geology, University of Keele, Keele, taffs ST5 5BG, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

During early Ordovician times volcanic and high-level intrusive activity occurred at numerous centres across North Pembrokeshire. Previous work suggested a geochemical transition in this activity from calcalkaline through to tholeiitic with time. However, new data indicate more extensive calc-alkaline magmatism and that both magma types were coeval. The origin of the calcalkaline magmas remains equivocal, but the tholeiitic magmas appear to have been derived from a source similar to N-type MORB, variably modified by supra-subduction zone fluids, combined with some fractionation during ascent. These data are consistent with emplacement in a supra-subduction zone marginal basin.

Information

Type
Articles
Information
Geological Magazine , Volume 129 , Issue 5 , September 1992 , pp. 615 - 624
Copyright
Copyright © Cambridge University Press 1992

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Article purchase

Temporarily unavailable

References

Allen, P. M., Cooper, D. C., Bide, P., Cameron, D. G., Parker, M. E., Haslam, H. W., Easterbrook, G. D. & Basham, I. R. 1985. Exploration for porphyry-style copper mineralisation near Llandeloy, southwest Dyfed. Mineral Reconnaissance Programme Report, British Geological Survey, No. 78.Google Scholar
Bates, D. E. B., Bromley, A. V. & Jones, A. S. G. 1969. The geology of the Bishops and Clerks Islands, Pembrokeshire. In The Pre-Cambrian and Lower Palaeozoic rocks of Wales (ed. Wood, A.), pp. 447–9. University of Wales Press.Google Scholar
Bevins, R. E. 1978. Pumpellyite-bearing basic igneous rocks from the Lower Ordovician of North Pembrokeshire, Wales. Mineralogical Magazine 42, 81–3.Google Scholar
Bevins, R. E. 1982. Petrology and geochemistry of the Fishguard Volcanic Complex, Wales. Geological Journal 17, 1–21.CrossRefGoogle Scholar
Bevins, R. E. & Roach, R. A. 1979. Early Ordovician volcanism in Dyfed, S. W. Wales. In The Caledonides of the British Isles - reviewed (eds Harris, A. L. C. H. Holland, and Leake, B. E.), pp. 603–9. Special Publication of the Geological Society of London No. 8.Google Scholar
Bevins, R. E. & Roach, R. A. 1982. Ordovician igneous activity in south-west Dyfed. In Geological excursions in Dyfed, south-west Wales (ed. Bassett, M. G.), pp. 65–80. National Museum of Wales, Cardiff.Google Scholar
Bevins, R. E. & Rowbotham, G. 1983. Low-grade metamorphism within the Welsh sector of the paratectonic Caledonides. Geological Journal 18, 141–68.Google Scholar
Bevins, R. E., Kokelaar, B. P. & Dunkley, P. N. 1984. Petrology and geochemistry of lower to middle Ordovician igneous rocks in Wales: a volcanic arc to marginal basin transition. Proceedings of the Geologists' Association 95, 337–47.CrossRefGoogle Scholar
Bevins, R. E., Lees, G. J. & Roach, R. A. 1989. Ordovician intrusionsm of the Strumble Head-Mynydd Preseli region, Wales: lateral extensions of the Fishguard Volcanic Complex. Journal of the Geological Society, London 146, 113–23.CrossRefGoogle Scholar
Bevins, R. E., Lees, G. J. & Roach, R. A. 1991. Ordovician bimodal volcanism in SW Wales: geochemical evidence for petrogenesis of the silicic rocks. Journal of the Geological Society, London 148, 719–29.Google Scholar
Cox, A. H. 1915. The geology of the district between Abereiddy and Abercastle. Quarterly Journal of the Geological Society of London 71, 273–340.CrossRefGoogle Scholar
Elsden, J. V. 1905. On the igneous rocks occurring between St David's Head and Strumble Head, Pembrokeshire. Quarterly Journal of the Geological Society of London 61, 579–607.CrossRefGoogle Scholar
Evans, W. D. 1945. The geology of the Prescelly Hills, North Pembrokeshire. Quarterly Journal of the Geo Geological Society of London 101, 89–107.Google Scholar
Fortey, R. A. & Owens, R. M. 1978. Early Ordovician (Arenig) stratigraphy and faunas of the Carmarthen district, south-west Wales. Bulletin of the British Museum (Natural History) 30, 225–94.Google Scholar
Fortey, R. A. & Owens, R. M. 1987. The Arenig Series in South Wales. Bulletin of the British Museum (Natural History) 41, 69–307.Google Scholar
Kokelaar, B. P., Howells, M. F., Bevins, R. E., Roach, R. A. & Dunkley, P. N. 1984. The Ordovician marginal basin of Wales. In Marginal Basin Geology: Volcanic and associated sedimentary and tectonic processes in modern and ancient marginal basins (eds Kokelaar, B. P. and Howells, M. F.), pp. 245–69. Special Publication of the Geological Society of London, No. 16.Google Scholar
Kokelaar, B. P., Bevins, R. E. & Roach, R. A. 1985. Submarine silicic volcanism and associated sedimentary and tectonic processes, Ramsey Island, SW Wales. Journal of the Geological Society, London 142, 591–613.Google Scholar
Leat, P. T. & Thorpe, R. S. 1986. Geochemistry of an Ordovician basalt-trachybasalt-subalkaline/peralkaline rhyolite association from the Lleyn Peninsula, North Wales, U.K. Geological Journal 21, 29–43.Google Scholar
Leat, P. T., Jackson, S. E., Thorpe, R. S. & Stillman, C. J. 1986. Geochemistry of bimodal basalt-subalkaline/peralkaline rhyolite provinces within the Southern British Caledonides. Journal of the Geological Society, London 143, 259–73.Google Scholar
Lees, G. J., Roach, R. A., Shufflebotham, M. M. & Griffiths, N. G. 1987. Upper Proterozoic basaltic volcanism in the Northern Massif Armoricain, France. In Geochemistry and Mineralization of Proterozoic Volcanic Suites (eds Pharaoh, T. C., Beckinsale, R. D. and Rickard, D.), pp. 503–23. Special Publication of the Geological Society of London no. 33.Google Scholar
Lowman, R. D. W. & Bloxam, T. W. 1981. The petrology of the Lower Palaeozoic Fishguard Volcanic Group and associated rocks E of Fishguard, N Pembrokeshire (Dyfed) South Wales. Journal of the Geological Society, London 138, 47–68.CrossRefGoogle Scholar
Merriman, R. J., Bevins, R. E. & Ball, T. K. 1986. Petrological and geochemical variations within the Tal y Fan Intrusion: a study of element mobility during low-grade metamorphism with implications for petrotectonic modelling. Journal of Petrology 27, 1409–36.Google Scholar
Nakamura, N. 1974. Determination of REE, Ba, Fe, Mg, Na, and K in carbonaceous and ordinary chondrites. Geochimica et Cosmochimica Acta 38, 757–75.Google Scholar
Parkinson, J. 1897. Some igneous rocks in north Pembroke-shire. Quarterly Journal of the Geological Society of London 53, 465–76.Google Scholar
Part, G. M. 1922. Notes on the Ordovician lavas of the Mynydd Prescelly, North Pembrokeshire. Geological Magazine 54, 310–23.CrossRefGoogle Scholar
Pearce, J. A. 1983. Role of the sub-continental lithosphere in magma genesis at active continental margins. In Continental basalts and mantle xenoliths (eds Hawkesworth, C. J. and Norry, M. J.), pp. 230–49. Shiva, Nantwich.Google Scholar
Roach, R. A. 1969. The composite nature of the St David's Head and Carn Llidi Intrusions of North Pembrokeshire. In The Precambrian and Lower Palaeozoic Rocks of Wales (ed. Wood, A.), pp. 409–33. University of Wales Press.Google Scholar
Robinson, D. & Bevins, R. E. 1986. Incipient metamorphism in the Lower Palaeozoic marginal basin of Wales. Journal of Metamorphic Petrology 4, 101–13.Google Scholar
Robinson, D., Nicholls, R. A. & Thomas, L. J. 1980. Clay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, South Wales. Mineralogical Magazine 43, 857–63.CrossRefGoogle Scholar
Saunders, A. D. & Tarney, J. 1991. Back-arc basins. In Oceanic Basalts (ed. Floyd, P. A.), pp. 219–63. Blackie & Son, Glasgow.Google Scholar
Thomas, H. H. & Cox, A. H. 1924. The volcanic series of Trefgarn, Roch and Ambleston (Pembrokeshire). Quarterly Journal of the Geological Society of London 122, 45–62.Google Scholar
Thorpe, R. S., Leat, P. T., Bevins, R. E. & Hughes, D. J. 1989. Late-orogenic alkaline/subalkaline Silurian volcanism of the Skomer Volcanic Group in the Caledondies of Wales. Journal of the Geological Society, London 146, 125–32.Google Scholar
Trench, A., McKerrow, W. S. & Torsvik, T. H. 1991. Ordovician magnetostratigraphy: a correlation of global data. Journal of the Geological Society, London 148, 949–57.Google Scholar
Williams, T. G. 1934. The Pre-Cambrian and Lower Palaeozoic rocks of the eastern end of the St David's Pre-Cambrian area, Pembrokeshire. Quarterly Journal of the Geological Society of London 90, 32–75.Google Scholar
Wood, D. A. 1980. The application of the Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary province. Earth and Planetary Science Letters 50, 11–30.CrossRefGoogle Scholar